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(about 10 km) the average precipitation would be 8.3 in.., almost twice the observed amount. This calculation suggests that a substantial amount of excess SL W was transported over the Plateau as has been found over other mountain barriers in the intermountain West (e.g., Super and Huggins 1993). The portion of excess SL W that cloud seeding can convert to precipitation has yet to be demonstrated. However, the "raw material" needed for seeding to be effective certainly exists in relative abundance. The availability of abundant SL W has been assumed for decades but has been verified only in the past several years. The 1991 data set also raises questions about the effectiveness of the Utah operational seeding program. Physical reasoning was presented that suggested seeding rates may be too low, at least for warmer storms. Admittedly, the estimates of effective IN may be flawed by instrumentation limitations and possible unrepresentativeness of CSU generator calibrations for winter orographic clouds. However, in the absence of better information, the observations and calculations presented in this paper indicated there is reason to be concerned. Production of adequate concentrations of seeded ice particles is basic to successful seeding. This topic deserves further investigation in the Utah operational program in particular, and in seeding programs in general. The main problem for the Utah operational seeding program appears to be the relatively warm SL W temperatures combined with the strong temperature dependence of AgI as an effective IN. This problem could be partially remedied by increasing the source strength of potential IN using improved seeding generators and solutions and higher AgI output rates. However, the SL W is probably too warm for effective seeding with any practical AgI solution and seeding rate some of the time. Even transporting the AgI to higher, colder altitudes by aircraft seeding would frequently be ineffective because the AgI would then be above the SL W needed to nucleate ice crystals. This is not to suggest that more effective AgI solutions and higher output generators should not be employed. Anything done to increase the output of effective IN should help seeding effectiveness. However, practical limits exist regarding what can be done with AgI. A large fraction of the winter storms, tending to be those with highest SL W amounts, likely cannot be effectively seeded with present AgI solutions because the SL W is simply too warm:. The problem of seeding warm SL W. with AgI is not unique to Utah. The statistic.al analysis of Super and Heimbach (1983) strongly suggested that the warmer, wetter half of Montana winter orographic storms did not respond to AgI seeding, but the colder, drier storms (<-9 oC at 2600 m) clouds did respond. The State of California has been developing a propane seeding technology because the warm SL W problem is severe there (Reynolds, 1991). Propane seeding can create high concentrations of ice crystals at temperatures colder than 0 oC. Remote-controlled propane dispensers are much more economical than remote-controlled AgI generators, and are more reliable because they are much simpler devices. However, they must be located in or very near clouds to be effective. It is recommended that the State of Utah pursue a number of approaches aimed at increasing the effectiveness of the operational seeding program. High output generators and more effective AgI solutions should be considered. Higher altitude release sites would increase the frequency of targeting SL W clouds. The possibility of high altitude releases from mountains upwind from the target areas deserves further exploration. Ongoing analysis suggests that AgI releases above canyon mouths may be more effective than AgI releases from valley floor locations. Finally, propane seeding should receive serious attenti~n because even warm storms can be seeded as long as the propane dispensers are located at high altitudes within the orographic cloud. 53